Volvo in the 90's used a similar system, 10 turns or so around a reed switch to one headlight, and then another 10 turns in the opposite direction to cancel out the magnetic field to the other headlight, if one of the bulbs went the fields no longer cancelled, the reed switch was activated and on came a warning light on the dash, simple and reliable.
Make something up and try different numbers of turns untill the right sort of current level is reached before the switch pulls in.
You could use 2 such devices, one for early warning and another to disconnect the power for a period of time.